High voltage direct current transmission grids for transmitting energy on a large scale are regaining attention for various reasons. The re-advent of DC grids is strongly linked to a different concept of how to drive power into the DC grid. Future DC grids may be controlled by a voltage controlled source, also known as voltage source converters (VSC). In such grids, a fault current may rise very fast in case of a short circuit and as a result may burden the system reliability.
In the event of a short circuit in a known AC grid, an interrupt concept may benefit from the alternating properties of the AC in the grid. When opening an associated circuit breaker in an AC current path, an electric arc may electrically connect such circuit breaker electrodes and may continue to allow an electric arc current to cross the circuit breaker. However, due to the nature of the AC driving source, such ongoing electric arc current in the AC current path may oscillate, too, and inherently may show current zero crossings. A zero crossing in current is desired for extinguishing the electric arc and for stopping the current flow across the circuit breaker completely.
In DC grids, however, no such current zero crossing occurs as a consequence of the driving source, but a current zero in the DC current path is desired to be generated by other means when or after the circuit breaker is brought to its open state. In one approach, a current zero is caused by injecting an oscillating growing counter-current into the DC current path. Such oscillating counter-current may at one point in time compensate for the electric arc current and may finally cause at least a temporary current zero in the DC current path which in turn may be used for extinguishing the electric arc. A means for evoking an oscillating counter-current may be a resonance circuit arranged in parallel to the circuit breaker. Such circuit breaker is more generally denoted in the following text as switching element. However, after connecting the resonance circuit in parallel to the switching element, a certain time must be lapsed before the oscillating counter-current reaches a magnitude sufficient to compensate for the electric arc current across the switching element: this will be hereinafter referred to as time to Current Zero (tCZ).
DE 2 039 065 refers to a circuit breaker arrangement in which the current is first commutated from the main path into an ohmic resistance path prior to being commutated into an absorber path. For building such ohmic resistance path affecting the main path, the circuit breaker is split into at least two circuit breakers, one of which may be switched to shunt the ohmic resistance which upon switching explodes in view of the high currents applied. This event, in turn, makes the current commutate into the absorber path.